Automated sampling systems are known for handling multiple sample sources, such as a tray with a plurality of vials with samples for processing in a liquid chromatography system. Generally, in such systems samples are stored in vials that are in turn stored on trays. The systems include transport facilities for transporting the sample vials to a sampling station, by positioning the trays under the sampling station and rotating the trays positioning each of the individual vials, one at a time, beneath the sampling station for sampling. Known systems typically involve a belt drive mechanism in the transport system.
For instance, U.S. Pat. No. 4,622,457 ("the 457 patent") describes an autosampler mechanism that positions a tray of sample vials beneath a sampling station and lifts each vial individually from the tray for sampling by a stationary sampling mechanism or needle. The sample vials are transported to and away from the sampling station by a transport system that includes a rotatable platter and four planetary trays carried by the rotatable platter.
A belt driven clutch and brake drive system described in the '457 patent facilitates rotation of the rotatable platter, and rotation of the trays relative to the rotatable platter so that any sample vial can be positioned beneath the sample station. The clutch and brake drive system requires an elaborate arrangement of drive shafts, pulleys and a drive belt to effect rotation of the platter and trays. A clutch electromagnet and an electromagnetic brake are also implemented in the '457 patent to effect three modes of operation: a braked mode wherein the tray mechanism is in a fixed, braked position; a platter rotation mode wherein the platter is rotated to rotate the four planetary trays in order to position a selected tray beneath the sampling station; and a tray rotation mode wherein the platter is fixed but the trays are rotated with respect to the platter.
Positioning of the sample vials in the '457 device is effected by an optical sensor located inside the sample compartment. Samples can be identified by slot location in the tray in accordance with "identifying elements" located under each slot. Each tray has an orientation spot located on its outer periphery for reading by the optical sensor. Location of the optical sensor(s) in the sample compartment presents a problem in that when the sample compartment is cooled moisture build-up can occur on the sensors and can cause the sensor to misread or not read at all.
Known systems such as disclosed in the '457 patent disadvantageously require lifting of the samples which unnecessarily agitates the sample vials. The elaborate clutch and pulley drive system disadvantageously requires many components that add significant cost to the system and take up significant amounts of space. The belt is subject to wear, misalignment and loosening over time which results in a need for frequent maintenance and repair. Furthermore, due to belt flexing and other mechanical phenomena, the belt and pulley system exerts unbalanced forces on the platter and trays which may cause inaccuracies in positioning and/or excessive vibration of the platter and trays resulting in further unnecessary agitation of the sample vials. Additionally, the expansion or reconfiguration of such a system by the addition of trays to a platter is extremely difficult and would likely exacerbate the disadvantages and problems described hereinabove, because a longer belt and additional pulleys would be required. Thus, the system of the '457 patent is seemingly limited in terms of sample capacity (to 80 samples: 4 trays times 20 samples per tray).
Other sample transport systems are known in the art, such as ones implemented in Model 712 and 717 Autosampler systems manufactured by Waters Chromatography (presently Waters Corporation), formerly a division of Millipore Corporation. Although free of the overly complex, costly and space consuming pulleys and clutch and brake mechanisms of some sample transport systems known in the art, the transport systems of the Model 712 and 717 Autosampler systems nonetheless incorporate belt driven actuators. Belt driven systems, as discussed, suffer disadvantages associated with the flexing and wear of the belt. Additionally, the Model 712 and 717 systems include an optical sensor located in the sample compartment for identifying the location of samples. Again, moisture build-up can occur on sensors located in the sample compartment which may cause the sensor to misread or to not read at all. Furthermore, the prior art Water's devices actuated a large, single carousel with a limited capacity of 48 or 96 sample vials.